Hydrogen is a clean energy carrier for replacing petroleum fuels to relieve issues associated with global warming. Water splitting by eletrolyzer is one of the most promising and efficient methods to produce hydrogen on demand. Among many different cathode materials, pure Platinum (110) exhibits the highest efficiency in the hydrogen evolution reaction (HER), where its Tafel slope is as low as ˜30 mV/dec. However, the high cost and limited source of Pt retards its large scale applications. Recent research efforts have focused on several more economical materials which may be suitable replacements for Pt cathodes, such as molybdenum sulfide, Mo2C, MoB, MoN and metal phosphides. It is recently noted that the HER efficiency of transition metal phosphides of Mo, W, Fe, Co and Ni have shown significant advances. The content for Fe, Ni, Co, Mo and Pt in the Earth's crust is estimated to be 50000, 80, 20, 1.5 and 0.003 ppm respectively. It is apparent that Fe, the fourth most common element in the Earth's crust, is a very attractive material for large-scale catalysis. Hence, the possibility of using iron phosphide as a HER catalyst has been extensively studied. FeP2 was obtained by the pyrolysis of ferrocene and red phosphorous. Nanoporous FeP nanosheets were prepared by ion-exchange synthesis using Fe18S25 and trioctyl-phosphine as sources. Alternatively, FeP nanoparticles were synthesized by gas phase phosphidation of Fe3O4 nanoparticles at 350° C. These reports have demonstrated a Tafel slope ranging from 59 to 67 mV/dec. Very recently, dense FeP nanowire array has been achieved by chemical phosphidation of the hydrothermally grown FeOOH nano array, where the Tafel slope of the system has been further lowered to 38 mV/dec.